On the use of the WLF model in polymers and foods.

The validity of the WLF model with fixed "universal" coefficients was tested against that of the model original form with variable coefficients using published coefficients of polymers and amorphous sugars crystallization and viscosity data. The disagreement between the two versions of the model is particularly large at temperature ranges starting about 20 to 30 degrees K above the glass transition or reference temperature, excluding the former from being a model of general applicability. Because the WLF model mathematical structure entails the existence of an almost linear region near the reference temperature, establishment of its validity as a kinetic model and meaningful determination of its constants requires data spread over an extended temperature range, especially when the experimental results have a scatter.